1. Field of the Invention
This invention relates to a method for analyzing the anisotropy of a given substance and an apparatus for analyzing the anisotropy of the given substance which take advantage of optical interference, particularly to an anisotropy analyzing method and an anisotropy analyzing apparatus preferably usable for the anisotropy observation in a stress condition of a viscoelastic fluid.
2. Description of the Prior Art
Conventionally, for measuring and analyzing an anisotropy such as a difference in normal stresses of a viscoelastic fluid, a light beam is modulated electrically or mechanically to generate plural light beams alternately in time of which the planes of polarization are orthogonal each other. Then, the thus obtained plural light beams are introduced into the viscoelastic fluid, and are analyzed after passing through the viscoelastic fluid. Therefore, for detecting the transmitted plural light beams as an output signal, it is required that the plural light beams are synchronized electrically before the introduction.
As a result, the measuring system becomes complicated entirely and requires expensive instruments. Moreover, the above anisotropy measuring method can not measure the anisotropy in a given area at the same time.
It is an object of the present invention to provide a new anisotropy analyzing method which can measure an anisotropy of a given substance in a given area at the same time and an anisotropy analyzing apparatus to be preferably employed in the anisotropy analyzing method.
For achieving the above object, this invention relates to an anisotropy analyzing method comprising the steps of:
preparing two light beams having the same wavelength of which the plane of polarization are crossed at a given angle,
introducing the two light beams into a sample to be measured in anisotropy at the same time,
rotating the plane of polarization of one of the two light beams by the given angle so as to correspond to that of the other of the two light beams, after passing the two light beams through the sample,
superimposing the two light beams, and
observing an interference pattern of the thus obtained superimposed light beam.
That is, in the anisotropy analyzing method of the present invention, first of all, two light beam are generated continuously in time of which the planes of polarization are crossed at a given angle, which is different from the above conventional method. Then, the two light beams are introduced into a sample to be measured in anisotropy at the same time, and are superimposed after passing through the sample so that their planes of polarization corresponds each other. Then, the interference pattern of the superimposed light beam is observed.
If the sample has an anisotropy such as a stress difference, at least one of the two light beams of which the planes of polarization are crossed each other is changed in refractive index because of the anisotropy. Therefore, the interference pattern of the anisotropic sample is shifted from that of a non-anisotropic sample. Consequently, the anisotropy of the sample can be measured qualitatively by observing the interference pattern shift.
Moreover, if the parameters relating the interference pattern shift to the anisotropy of the sample are known, the anisotropy can be measured quantitatively.
As mentioned above, since in the anisotropy analyzing method of the present invention, the two light beams which are continuous in time and of which the planes of polarization are crossed at a given angle are employed, the conventional electric synchronization for the plural light beams is not required. Therefore, the measuring system can be simplified entirely, and does not require expensive instruments, so that the cost of the total measuring system can be reduced. Moreover, since the two light beams are introduced into the sample, and irradiated to a given area of the sample at the same time, the anisotropy around the given area of the sample can be measured at the same time.
Moreover, the anisotropy of the sample can be measured without the density fluctuation due to the temperature change and pressure change of the sample, and the momentary structural change can be also measured.
In a preferred embodiment of the present invention, the two light beams having their respective crossing planes of polarization are superimposed before they are introduced into the sample, and the thus obtained superimposed light beam is introduced into the sample. Thereby, the anisotropy of the sample can be measured easily over the traveling direction of the light beam, for example, over the thickness direction of the sample.
In another preferred embodiment of the present invention, the two light beams having their respective crossing planes of polarization are introduced into the sample so that their beam directions are crossed each other by a small angle. In this case, the two light beams are crossed at a given position inside the sample.
The anisotropy measuring apparatus of the present invention, for realizing the above measuring method, comprises:
before a sample to be measured in anisotropy,
a laser source to generate and oscillate a light beam to be used in anisotropy analysis
a light beam-dividing means to divide a light beam from the laser source into two light beams, and
a first plane of polarization-rotating means to rotate the plane of polarization of one of the thus obtained two divided light beams by a given angle,
after the sample to be measured in anisotropy,
a second plane of polarization-rotating means to rotate the plane of polarization of the one or the other of the two divided light beams by the given angle so that their planes of polarization can correspond each other,
a light beam-superimposing means to superimpose the two divided light beams, and
a light beam-projecting means to project and observe an interference pattern of the thus obtained superimposed light beam.
In the case of introducing the superimposed light beam into the sample according to the above preferred embodiment of the anisotropy measuring method, the anisotropy measuring apparatus has additional light beam-superimposing means to superimpose the divided light beams after the first plane of polarization-rotating means before the sample to be analyzed in anisotropy.
A half-wave plate may be preferably employed as the plane of polarization-rotating means. Since the half-wave plate is available in low cost, the use of the half-wave plate can reduce the cost of the total apparatus. In this case, since the plane of polarization of the one divided light beam is rotated by 90 degrees, it can measure the anisotropy of the sample in the orthogonal direction with the other divided light beam.
Moreover, this invention relates to an anisotropy analyzing method comprising the steps of:
preparing a single polarized light beam,
introducing the single polarized light beam into a sample to be measured,
dividing the single polarized light beam into two light beams, after passing through the sample,
superimposing the two divided light beams, and
observing an interference pattern of the thus obtained superimposed light beam.
In the above anisotropy analyzing method of the present invention, the two light beams of which the planes of polarization are crossed at a given angle are employed to analyze the anisotropy of the sample, but in this anisotropy analyzing method of the present invention, a single plane polarized light beam, a single circularly polarized light beam or a single elliptically polarized light beam is employed.
In this case, since the single polarized light beam is divided into the two light beams after passing through the sample, and the two divided light beams are superimposed, the anisotropy of the sample can be measured from the observation of the interference pattern of the superimposed light beam.